Re: [Xen-devel] Is there an issue with turning off "scrubbing free RAM" on boot with Xen 4.1.3

[Matt Wilson <msw@xxxxxxxxx>]

On Thu, Oct 10, 2013 at 10:42:14AM +0100, Andrew Cooper wrote:
> On 09/10/13 19:24, Roddy Rodstein wrote:

[...]

> > Could you please share your comments about turning of RAM scrubbing,
> > i.e. have you seen any consequences, security issues and/or threats,
> > red flags, etc...?

[...]

> In the Xen model, domains are responsible for clearing any sensitive
> data they have out of memory before shutdown.

This isn't strictly true. Memory is scrubbed by Xen when the domain
cannot do it for itself (i.e., when a domain is dying during
shutdown). However by default domains /are/ responsible for scrubbing
pages that are returned to Xen via a reservation adjustment (i.e.,
pages returned via the balloon driver).

--msw

> The bootscrub is a preventative measure to ensure that after a crash,
> stale domain information is cleared from RAM before that RAM is reused
> for a new VM.
> 
> If this is not a concern for you, then you can easily turn bootscrub off
> by adding "no-bootscrub" to the Xen command line.

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